A conventional Power over Ethernet (PoE) system includes power sourcing equipment (PSE) and one or more powered devices (PDs) that connect to the PSE through cabling (e.g., CAT5, CAT5e, CAT6, etc.). IEEE 802.3af-2003 is a standard for delivering up to 12.95 Watts to a PD. IEEE 802.3at-2009 is a standard for delivering up to 25.5 Watts of power to a PD.
Before the PSE delivers any power to a PD through one of its ports, the PSE typically performs a discovery operation through that port. For example, if the PSE does not detect a particular impedance which identifies the PD as a device which can receive power through that port, the PSE does not deliver power through that port thus preventing damage to the device. However, if the PSE detects the particular impedance through that port, the PSE delivers power to the PD through that port. IEEE 802.3af-2003 (PoE) and IEEE 802.3at-2009 (PoE Enhancements) provide additional detection and classification details.